GLUTAMATE-GATED CHLORIDE CHANNEL WITH GLUTAMATE-TRANSPORTER-LIKE PROPERTIES IN CONE PHOTORECEPTORS OF THE TIGER SALAMANDER

1. Using the patch-clamp technique, we investigated whether the glutam ate-elicited current in mechanically isolated cone photoreceptors from the salamander retina is generated by a Cl- channel or a glutamate tr ansporter. 2. The current reversed near the equilibrium potential for Cl-, was decreased by three Cl- channel blockers, 5-nitro-2-(3-phenyl- propylamino) benzoic acid, 4,4'-diisothiocyanostilbene-2,2'-disulfonat e, and diphenylamine 2,2'-dicarboxylic acid, and was eliminated when g luconate was substituted for both internal and external Cl-, features consistent with the current being mediated by a Cl- channel. 3. The si ngle-channel conductance of the Cl- channel was estimated by noise ana lysis of the glutamate-elicited current fluctuations to be 0.7 pS with an open time of 2 ms. 4. The magnitude of the current was dependent o n both internal and external Na+ and K+, features consistent with the current being related to the activation of a glutamate transporter. Ye t changes in their concentrations did not affect the reversal potentia l of the current. 5. Taken together with earlier reports on this curre nt showing a that it has a glutamate-transporter-like pharmacology, ou r results suggest that the glutamate-elicited current is carried by a Cl- channel but gated by a glutamate receptor whose pharmacology and i onic requirement resemble those previously described for glutamate tra nsporters.